ABSTRACT
At present, scrap tires are converted into so-called "crumb rubber'' by either ambient or cryogenic grinding. Because of the high cost of liquid nitrogen used as a refrigerant in the cryogenic method, size reduction at an ambient temperature is used more often for coarse powder production. Tires are shredded into chips about 0.75-in long. This is followed by a magnetic separation of steel and removal of textile cord. The rubber chips are then reduced to rougher, smaller pieces by different milling devices in a series of screening and re-grinding operations to achieve the desired particle size. For the traditional rubber "reclaim," crumb rubber is mixed with water, oil, and chemicals and is then heated under pressure. During this process, the carbon-sulfur bonds are ruptured, and the rubber becomes mostly devulcanized, so it is then capable of being shaped into slabs. These slabs are used by tire manufacturers as an alternative to virgin rubber for re-use in new tires or as an ingredient in other rubber products. Because reclaimed rubber has reduced elasticity, it is currently used for only about five percent of all new-tire production.
